TO THE EDITOR
We read with great interest the review titled “Liquid biopsy in cholangiocarcinoma: Current status and future perspective” by Rompianesi et al, and we believe that liquid biopsy (LB) has opened new avenues for personalized medicine in patients with cholangiocarcinoma (CCA). This review summarizes the present challenges of diagnosing, managing and monitoring CCA and the unique advantage of LB for these challenges. The authors conclude that a growing body of research supports the idea that LB can overcome the difficulties of traditional tools and might be particularly helpful in detecting early cancer, identifying therapeutic targets, predicting treatment response, and monitoring the genetic profile of CCA.
CCA is an aggressive biliary malignancy originating from cholangiocytes along the biliary tree, excluding the gall bladder and the Vater ampulla. CCA is usually asymptomatic in the early stages. Therefore, the majority of CCA patients are generally diagnosed at an advanced stage. Because there are limited therapeutic options, advanced CCA has a dismal prognosis[3,4]. Even for patients with localized early disease who can benefit from surgery, the high recurrence rate may cause an inferior clinical outcome. Despite recent advances in systemic chemotherapy, targeted therapy, and immunotherapy, the prognosis of patients with advanced unresectable CCA remains disappointing because of tumour heterogeneity and the variability of treatment response. As the recognition of the importance of precision medicine by clinicians is growing, there is an urgent need for new, accurate tools for early cancer detection, monitoring of the tumour molecular profile, real-time assessment of therapeutic efficacy, and identification of therapeutic targets and resistance mechanisms in CCA.
Tumours can release their contents along with genetic material into body fluids such as blood, urine, saliva, bile, and cerebrospinal fluid. LB is a novel, minimally invasive, and safe method for detecting tumour components in body fluids, including circulating tumour cells, circulating tumour DNA (ctDNA), circulating cell-free RNA, extracellular vesicles, and tumour-educated platelets. Advances in the detection and characterization of ctDNA have enabled LB to be rapidly translated into the management of patients with advanced solid tumours. With the development of next-generation sequencing and oncology genomics assessment, researchers can identify and analyse a wealth of cancer genetic markers that contribute to the occurrence, progression and heterogeneity of cancer. Analysing genetic markers or the molecular profile of solid cancers traditionally relies on tissue biopsy. However, limited accessibility to tumour samples and tumour heterogeneity present challenges for acquiring representative tumour samples throughout the disease course. As a less invasive approach, LB can be used to track spatial and temporal heterogeneity and monitor dynamic changes in tumour biology at the molecular and genetic levels.
LB samples (in most cases, blood) are easy to obtain, and LB can be repeated in patients, enabling real-time molecular monitoring of CCA. LB approaches can also be used to detect abnormalities before imaging examinations. As previously reported, the detection of ctDNA precedes the radiological detection of early tumour recurrence by 3–5 mo in several cancers[11,12]. Furthermore, LB can be used to guide clinical treatment and monitor the treatment response. Among patients with biliary tract cancers who received systemic treatment after ctDNA analysis and drug matching, the matched targeted regimens showed longer progression-free survival and a better disease control rate than unmatched methods. Characterized, therapeutically relevant ctDNA alterations can also be found in CCA patients after gene-targeted therapy. Furthermore, since ctDNA may include DNA shed into the bloodstream from both primary and metastatic tumours, the genomic alterations of ctDNA can reflect the cancer heterogeneity of the whole body better than those found in tissue biopsy[14,15]. Cancer heterogeneity may be part of the reason for the unfavourable outcomes of several gene-targeted trials in CCA.
There remain several challenges for the clinical application of LB. The low concentration of ctDNA and difficulty in identifying ctDNA in peripheral blood may limit the accuracy of detection. There are also high sensitivity and specificity requirements of detection methods. Since various ctDNA assays are available, more comprehensive cross-platform comparisons are needed to standardize the preanalytical and analytical procedures. Detectable genomic mutations are not always relevant to cancer biology or therapy, so ctDNA analysis and sequencing data should be carefully interpreted. The use of machine learning tools and artificial intelligence technology may efficiently aid the analysis of increasingly complex cancer LB data.
In conclusion, it is necessary to realize individualized therapy to improve the clinical prognosis of patients with CCA. As an easy method for assessing genetic material and molecular profiling, LB can play an important role in early cancer detection, tumour heterogeneity assessment, therapy selection, and prognostic stratification in CCA. Although challenges exist for the clinical application of LB, its potential represents a movement towards precision medicine and individualized therapy. The scarcity of clinical data suggests that larger and deeper studies to define and validate the diagnostic and therapeutic roles of LB in CCA are needed.